tor-browser

The Tor Browser
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XiphExtradata.cpp (2931B)

      1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
      2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
      3 /* This Source Code Form is subject to the terms of the Mozilla Public
      4 * License, v. 2.0. If a copy of the MPL was not distributed with this
      5 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
      6 
      7 #include "XiphExtradata.h"
      8 
      9 namespace mozilla {
     10 
     11 bool XiphHeadersToExtradata(MediaByteBuffer* aCodecSpecificConfig,
     12                            const nsTArray<const unsigned char*>& aHeaders,
     13                            const nsTArray<size_t>& aHeaderLens) {
     14  size_t nheaders = aHeaders.Length();
     15  if (!nheaders || nheaders > 255) return false;
     16  aCodecSpecificConfig->AppendElement(nheaders - 1);
     17  for (size_t i = 0; i < nheaders - 1; i++) {
     18    size_t headerLen;
     19    for (headerLen = aHeaderLens[i]; headerLen >= 255; headerLen -= 255) {
     20      aCodecSpecificConfig->AppendElement(255);
     21    }
     22    aCodecSpecificConfig->AppendElement(headerLen);
     23  }
     24  for (size_t i = 0; i < nheaders; i++) {
     25    aCodecSpecificConfig->AppendElements(aHeaders[i], aHeaderLens[i]);
     26  }
     27  return true;
     28 }
     29 
     30 bool XiphExtradataToHeaders(nsTArray<unsigned char*>& aHeaders,
     31                            nsTArray<size_t>& aHeaderLens, unsigned char* aData,
     32                            size_t aAvailable) {
     33  size_t total = 0;
     34  if (aAvailable < 1) {
     35    return false;
     36  }
     37  aAvailable--;
     38  int nHeaders = *aData++ + 1;
     39  for (int i = 0; i < nHeaders - 1; i++) {
     40    size_t headerLen = 0;
     41    for (;;) {
     42      // After this test, we know that (aAvailable - total > headerLen) and
     43      // (headerLen >= 0) so (aAvailable - total > 0). The loop decrements
     44      // aAvailable by 1 and total remains fixed, so we know that in the next
     45      // iteration (aAvailable - total >= 0). Thus (aAvailable - total) can
     46      // never underflow.
     47      if (aAvailable - total <= headerLen) {
     48        return false;
     49      }
     50      // Since we know (aAvailable > total + headerLen), this can't overflow
     51      // unless total is near 0 and both aAvailable and headerLen are within
     52      // 255 bytes of the maximum representable size. However, that is
     53      // impossible, since we would have had to have gone through this loop
     54      // more than 255 times to make headerLen that large, and thus decremented
     55      // aAvailable more than 255 times.
     56      headerLen += *aData;
     57      aAvailable--;
     58      if (*aData++ != 255) break;
     59    }
     60    // And this check ensures updating total won't cause (aAvailable - total)
     61    // to underflow.
     62    if (aAvailable - total < headerLen) {
     63      return false;
     64    }
     65    aHeaderLens.AppendElement(headerLen);
     66    // Since we know aAvailable >= total + headerLen, this can't overflow.
     67    total += headerLen;
     68  }
     69  aHeaderLens.AppendElement(aAvailable - total);
     70  for (int i = 0; i < nHeaders; i++) {
     71    aHeaders.AppendElement(aData);
     72    aData += aHeaderLens[i];
     73  }
     74  return true;
     75 }
     76 
     77 }  // namespace mozilla